[PATCH] D70500: [WebAssembly] Enable use of wasm-opt and LTO-enabled system libraries

Sat May 2 10:03:25 PDT 2020

sbc100 added a comment.

In D70500#1999934 <https://reviews.llvm.org/D70500#1999934>, @bernhard wrote:

> > Would it work to increase the memory size, and then put your data in the new space this creates at the end of memory?
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> > `__data_end` and `__heap_base` aren't things you can move around once the linker has defined them. Their values can be baked in elsewhere in the wasm module, so it's not safe in general to insert new memory in between them and shift things around.
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> My plan was to embed arbitrary sized files directly into the data memory after the wasm file was created. But I think you're right, it ends up only working with simple wasm programs, more complex code crashes somewhere during `__wasm_call_ctors` with the approach I took.

I think the way to embed data blobs in your final binary is to pass them to the linker as inputs.  There are various techniques listed here: https://csl.name/post/embedding-binary-data/.   I imagine not all them them will work with today's toolchain but we should strive to make those approaches work where possible.

> I guess custom sections would be the official route but I was hoping to avoid having to pass the entire data through JavaScript before it reaches WASM land.
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> Also I'm very sorry to have hijacked this patch discussion with something very different. If you have some more hints for me how I could accomplish this I'd very gladly hear them, but if this is the wrong place we should probably leave it at that. Thank you for your time!

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https://reviews.llvm.org/D70500